Read MultiMarkdown metadata tags from files and apply them as macOS tags

mmdtagstomacos.rb

#!/usr/bin/env ruby
# encoding: utf-8
#
# Read MultiMarkdown metadata tags from files and apply them as macOS tags
#
# Usage:
#   mmdtagstomacos.rb *.md

require 'shellwords'
mmd = '/usr/local/bin/multimarkdown'

def apply_tags(file, tag_array)
  raise "No tags" unless tag_array
  raise "Invalid file specified" unless File.exists?(file)
  plist = '<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0"><array>'
  plist += tag_array.map{|tag| "<string>#{tag}</string>"}.join('')
  plist += '</array></plist>'

  $stderr.puts("Tagging #{file} (#{tag_array.join(' ')})")
  %x{xattr -w com.apple.metadata:_kMDItemUserTags '#{plist}' #{Shellwords.escape(file)}}
end

ARGV.each do |file|
  file = File.expand_path(file)
  if File.exists?(file)
    mmd_tags = %x{#{mmd} -e tags #{Shellwords.escape(file)}}.strip

    if mmd_tags.length > 0
      # Handle any instances of tags in YAML/JSON array format, e.g. [tag1,tag2]
      mmd_tags.sub!(/^\[(.*?)\]$/,'\1')
      tag_array = mmd_tags.split(/,/).map{|t|
        # trim spaces
        t.strip!
        # Avoid shell characters causing issues
        Shellwords.escape(t)
      }

      apply_tags(file, tag_array)
    end
  end
end